Blood sucking parasitic infestation on animals, especially the infestation of pets by fleas, has been a continued problem in the art. On account of the complexity of the life cycle of the flea, none of the methods known to the prior art of controlling such parasites is entirely satisfactory, especially since these methods are directed primarily to the control of adult fleas in the coat of the host animal and do not take into account the different juvenile stages of the fleas existing in the animals coats as well as on the floor, on carpets, in bedding, on chairs, in the garden and in other places with which the infested animal usually comes into contact. Adult cat and dog fleas (Ctenocephalides felis and C. canis) live naturally in the coat of the cat or dog host. They feed on host blood and the females lay eggs in the coat. Since the eggs are not sticky, they quickly fall off and can be found on the floor, carpets, animals' beddings, chairs used by the pets, the garden, the backyard, etc.
Thus, the total environment of the animal is infested with flea eggs, which in about two days hatch into larvae. There are three larval stages, each lasting about three days. In the last stage the larvae spin cocoons and transform to pupae. Under optimum conditions, i.e., 33.degree. C. and 65% relative humidity, the eggs transform to pupae in about 8 to 10 days. After a further period of approximately 8 days, the pupae develop to young adult fleas in the cocoon still lying on the floor, the carpets, the beddings, the chairs, etc. The young adult fleas wait until they sense the presence of an acceptable host animal and then emerge and attempt to jump onto it. Thus, it takes at least three weeks for eggs to develop to young adults able to reinfest the host. However, the young adults can remain for months, possibly as long as one year, in the cocoon, and in addition, under suboptimum conditions, it can take 4 to 5 months for the eggs to develop into young adults. Fleas must have a blood meal in order to become sexually mature and therefore be able to reproduce. The blood must come from the correct type of host.
This long life cycle, occurring at sites other than on the animal, has important implications for flea treatment applied to host animals. Even if fleas in the coat of the animal can be controlled successfully, i.e., if all adult fleas are killed by an active ingredient, the cat or dog is nevertheless exposed for weeks or even months to the risk of reinfestation by the newly emerged adults present in the animal's environment.
Infestation of dogs and cats with fleas has several undesirable effects for the treated animals or the owner. Such undesirable effects may manifest themselves in the form of local irritation or annoying itching, often leading to scratching. Quite a high number of animals become allergic to flea saliva, resulting in very itchy and crusty lumps on the animal's body at the site of the bites. Normally these lumps reach a diameter of 3 mm or more and cause the animal to bite and scratch, leading to subsequent hair loss. The infested animals create a nervous reaction and become more and more unattractive and irritable.
Furthermore, animals which are infested by fleas are permanently exposed to the danger of being infected by Dipylidium, a tape worm which is transmitted by the fleas.
Flea infestation not only is extremely annoying for the infested animal, but also unpleasant for the owner who observes the unusual behavior of a pet which is ill, suffering, and in need of help. In the prolonged absence of a suitable host animal, newly hatched fleas on the floor are compelled to attack humans (although they are not capable of reproduction if human blood is their sole source of nutrition). Even in the presence of the dog or cat, the owner may be bitten by the fleas. Moreover, some humans may suffer from allergic skin diseases as a result of dog and cat fleas or their excrete.
A number of methods for the control of fleas are known, but these have various drawbacks. When using flea combs for example, the animal owner has no choice other than combing the animal intensively and frequently. Depending on the size of the animal, this may take from several minutes to an hour. Not every animal will always patiently put up with being combed, nor is every owner prepared to sacrifice his time for this operation.
The use of anti-flea shampoos in many cases is impossible since most cats and a large number of dogs simply refuse to be given a bath or they can only be given a bath when the owner resorts to using force, in which case water and shampoo will be splashed about. Furthermore, the effect of such bathing does not last for more than about a week and the laborious procedure then must be repeated. Similar problems are encountered when using dips or rinses. Even the use of dusting powders as a rule is not tolerated by the animal without resistance since it takes several minutes to treat the entire surface of the coat uniformly and some dust is bound to get into the mouth, nose, and eyes of the animal. Even in the case of careful application, it is impossible to prevent the powder from being inhaled by the animal or its owner. There is virtually no way for the owner to avoid a more or less intensive contact with the active ingredient.
When using sprays, an owner may experience an unpleasant surprise since most animals, particularly cats, take flight or react aggressively to the noise of the spray. Moreover, sprays have all the drawbacks mentioned above for powders and, in addition, they disperse even more finely in the atmosphere, which means that animals and their owners simply can not avoid inhaling them.
Fleas are frequently also controlled with flea collars which are very effective temporarily. A particular weakness of this method of treatment, however, is that it is normally effective in a very limited region of the animal's body. In general, 100% kill is achieved in the region of the neck and thorax; however, more remote parts of the body are hardly affected. Besides, many of these collars look unattractive and may also irritate the animal. Today medallions are available which can be attached to the collar and which are said to be active. These medallions are appealing to the eye, but their effectiveness is unsatisfactory since they do not come into sufficient contact with the animal's coat. Several anti-flea organophosphorus compounds are available in the form of spot-on formulations. These are applied to a limited spot on the coat. In general, they exhibit good short-term activity against adult fleas but when applied often, the compositions have problematic toxicity. Some organophosphorus compounds are administered orally but have narrow safety limits and must never be applied simultaneously with other organophosphorus compounds.
On the whole it can be said that it has always been the objective of previous methods to kill the adult flea. Some of these methods can be applied quite successfully to control adult fleas for a short period. A fact which has so far not been acknowledged is that, owing to the particular life cycle of fleas, dogs and cats will be repeatedly reinfested because, on the one hand, the animal can not avoid coming into contact with the flea eggs, flea larvae and juvenile and adult fleas on the floor or in its immediate vicinity and, on the other hand, many pets again and again come into contact with infested members of the same species. Constantly recurring reinfestation is not prevented by using conventional pesticides.